// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
 */

#include <linux/crc32.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/nvmem-provider.h>
#include <linux/of_reserved_mem.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

struct rmem {
        struct device *dev;
        struct nvmem_device *nvmem;
        struct reserved_mem *mem;
};

struct rmem_match_data {
        int (*checksum)(struct rmem *priv);
};

struct __packed rmem_eyeq5_header {
        u32 magic;
        u32 version;
        u32 size;
};

#define RMEM_EYEQ5_MAGIC        ((u32)0xDABBAD00)

static int rmem_read(void *context, unsigned int offset,
                     void *val, size_t bytes)
{
        struct rmem *priv = context;
        void *addr;

        if ((phys_addr_t)offset + bytes > priv->mem->size)
                return -EIO;

        /*
         * Only map the reserved memory at this point to avoid potential rogue
         * kernel threads inadvertently modifying it. Based on the current
         * uses-cases for this driver, the performance hit isn't a concern.
         * Nor is likely to be, given the nature of the subsystem. Most nvmem
         * devices operate over slow buses to begin with.
         *
         * An alternative would be setting the memory as RO, set_memory_ro(),
         * but as of Dec 2020 this isn't possible on arm64.
         */
        addr = memremap(priv->mem->base, priv->mem->size, MEMREMAP_WB);
        if (!addr) {
                dev_err(priv->dev, "Failed to remap memory region\n");
                return -ENOMEM;
        }

        memcpy(val, addr + offset, bytes);

        memunmap(addr);

        return 0;
}

static int rmem_eyeq5_checksum(struct rmem *priv)
{
        void *buf __free(kfree) = NULL;
        struct rmem_eyeq5_header header;
        u32 computed_crc, *target_crc;
        size_t data_size;
        int ret;

        ret = rmem_read(priv, 0, &header, sizeof(header));
        if (ret)
                return ret;

        if (header.magic != RMEM_EYEQ5_MAGIC)
                return -EINVAL;

        /*
         * Avoid massive kmalloc() if header read is invalid;
         * the check would be done by the next rmem_read() anyway.
         */
        if (header.size > priv->mem->size)
                return -EINVAL;

        /*
         *           0 +-------------------+
         *             | Header (12 bytes) | \
         *             +-------------------+ |
         *             |                   | | data to be CRCed
         *             |        ...        | |
         *             |                   | /
         *   data_size +-------------------+
         *             |   CRC (4 bytes)   |
         * header.size +-------------------+
         */

        buf = kmalloc(header.size, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        ret = rmem_read(priv, 0, buf, header.size);
        if (ret)
                return ret;

        data_size = header.size - sizeof(*target_crc);
        target_crc = buf + data_size;
        computed_crc = crc32(U32_MAX, buf, data_size) ^ U32_MAX;

        if (computed_crc == *target_crc)
                return 0;

        dev_err(priv->dev,
                "checksum failed: computed %#x, expected %#x, header (%#x, %#x, %#x)\n",
                computed_crc, *target_crc, header.magic, header.version, header.size);
        return -EINVAL;
}

static int rmem_probe(struct platform_device *pdev)
{
        struct nvmem_config config = { };
        struct device *dev = &pdev->dev;
        const struct rmem_match_data *match_data = device_get_match_data(dev);
        struct reserved_mem *mem;
        struct rmem *priv;

        priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;
        priv->dev = dev;

        mem = of_reserved_mem_lookup(dev->of_node);
        if (!mem) {
                dev_err(dev, "Failed to lookup reserved memory\n");
                return -EINVAL;
        }
        priv->mem = mem;

        config.dev = dev;
        config.priv = priv;
        config.name = "rmem";
        config.id = NVMEM_DEVID_AUTO;
        config.size = mem->size;
        config.reg_read = rmem_read;

        if (match_data && match_data->checksum) {
                int ret = match_data->checksum(priv);

                if (ret)
                        return ret;
        }

        return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
}

static const struct rmem_match_data rmem_eyeq5_match_data = {
        .checksum = rmem_eyeq5_checksum,
};

static const struct of_device_id rmem_match[] = {
        { .compatible = "mobileye,eyeq5-bootloader-config", .data = &rmem_eyeq5_match_data },
        { .compatible = "nvmem-rmem", },
        { /* sentinel */ },
};
MODULE_DEVICE_TABLE(of, rmem_match);

static struct platform_driver rmem_driver = {
        .probe = rmem_probe,
        .driver = {
                .name = "rmem",
                .of_match_table = rmem_match,
        },
};
module_platform_driver(rmem_driver);

MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
MODULE_LICENSE("GPL");